The level of social life on which a research questions is focused, such as individuals, groups, towns, or nations.

Units of Observation

The cases about which measures actually are obtained in a sample.

Ecological Fallacy

An error in reasoning in which incorrect conclusions about individual-level processes are drawn from group-level data.

Reductionalist Fallacy (Reductionalism)

An error in reasoning that occurs when incorrect conclusions about group-level processes are based on individual-level data. Also knwon as individualist fallacy.

Cross-sectional Research Design

A study in which data are collected at only one point in time.

Time Order

A criterion for establishing a casual relation between two variables. The variation in the presumed cause (the independent variable) must occur before the variation in the presumed effect (the dependent variable).

Longitudinal Research Design

A study in which data are collected that can be ordered in time; also defined as research in which data are collected at two or more points in time.

Repeated Cross-sectional Design (Trend Study)

A type of longitudinal study in which data are collected at two ore more points in time from different samples of the same population.

Fixed-sample Panel Design (Panel Study)

A type of longitudinal study in which data are collected from the same individuals -- the panel -- at two or more points in time. In another type of panel design, panel members who leave are replaced with new members.

Subject Fatigue

Problems caused by panel members growing weary of repeated interviews and dropping out of a study or becoming so used to answering the standard questions in the survey that they start giving stock or thoughtless answers.

Event-based Design (Cohort Study)

A type of longitudinal study in which data are collected at two or more points in time from individuals in a cohort.

Cohort

Individuals or groups with a common starting point. Examples include college class of 1997, people who graduated from high school in teh 1980s, General Motor employees who started work between the years 1990 and 2000, and people who were born in the late 1940s or 1950s (the "baby boom generation").

Nomothetic Causal Explanation

An explanation that identifies common influences on a number of cases or events.

Ceteris Paribus

Latin phrase meaning "other things being equal."

Causal Effect (Nomothetic Perspective)

When variation in one phenomenon, an independent variable, leads to or results, on average, in variation in another phenomenon, the dependent variable.

Example: Individuals arrested for domestic assault tend to commit fewer subsequent assualts than do similar individuals who are accused in the same circumstances but not arrested.

Counterfactual

The outcome that would have occured if the subjects who were exposed to the treatment actually were not exposed, but otherwise had had identical experiences to those they underwent during the experiment.

Idiographic Causal Explanation

An explanation that identifies the concrete, individual sequence of events, thoughts, or actions that resulted in a particular outcome for a particular individual or that led to a particular event; may be termed an individualist or historicist explanation.

Causal Effect (Idiographic Perspective)

When a series of concrete events, thoughts, or actions result in a particular event or individual outcome.

Example: An individual is neglected by her parents but has a supportive grandparent. She comes to distrust others, has trouble in school, is unable to keep a job, and eventually becomes homeless. She subsequently develops a supportive relationship with a shelter case manager, who helps her find a job and regain her housing (based on Hirsch 1989).

Association

A criterion for establishing a nomothetic causal relationship between two variables: Variation in one cariable is related to variation in another variable.

Nonsupriousness

A criterion for establishing a causal relation between two variables; when a relationship between two variables is not due to variation in a third variable.

Spurious Relationship

A relationship between two variables that is due to variation in a third variable.

Extraneous Variable

A variable that influences both the independent and dependent variables so as to create a spurious association between them that disappears when the extraneous variable is controlled.

Randomization

The random assignment of cases, as by the toss of a coin.

Random Assignment

A procedure by which each experimental subject is placed

Statistical Control

A method in which one variable is held constant so that the relationship between two (or more) other variables can be assessed without the influence of variation in the control variable.

Example: In a different study, Sampson (1987) found a relationship between rates of family disruption and violent crime. He then classified cities by their level of joblessness (the control variable) and found that same relationship between the rates of family disruption and violent crime among cities with different levels of joblessness. So the rate of joblessness could not have caused the association between family disruption and violent crime.

Mechanism

A discernable process that creates a causal connection between two variables.

Contextual Effects

Relationships among variables that vary among geographic units or other social settings.

Context

A focus of idiographic causal explanation; a particular outcome is understood as part of a larger set of interrelated circumstances.